1. Field of the Invention
The present invention relates to an image sensor, and more particularly, to an image sensor having improved image reproducibility.
2. Description of Related Art
An image sensor converts optical information into electrical signals. Recently, with the development of computer and communication industries, there is an increasing demand for highly-efficient image sensors in various fields such as digital cameras, camcorders, personal communication systems, game devices, surveillance cameras, microcameras for medical use, robots, and so on.
An image sensor includes a pixel array, in which unit pixels are arranged in a matrix form and convert incident light into an electrical signal. The pixel array further includes a peripheral circuit controlling each unit pixel and processing the electrical signal of the unit pixel. The peripheral circuit may process an optical image input to the pixel array in various manners, for example, in a rolling shutter mode for processing moving images and a single frame capture mode (SFCM) for processing still images.
In the rolling shutter mode, since optical images input to the pixel array in real time are sequentially read by row, each row in the pixel array is exposed at a different time. In an SFCM (single frame capture mode), an entire optical image input through electrical shuttering is simultaneously transmitted to a charge detector of the pixel array and a signal stored in the charge detector is read by row.
When light is continuously incident on the pixel array in the SFCM, excess charges occurring in a photoelectric converter overflow into the charge detector, which may cause distortion in an image. Since overflowing charges increase while rows are read out sequentially, image distortion increases due to a read-out time difference between, for example, the first row and the last row.
Moreover, a plurality of unit pixels sharing a charge detector use the charge detector in time division mode. Accordingly, a read-out time difference occurs between the pixel units sharing the charge detector, and thus image distortion due to a time difference between pixel units may occur.
Therefore, a need exists for an image sensor having improved image reproducibility.